Columbus to host worldwide sea traffic tracking experiment

AIS polar signal detection probabilities

18 September 2009

ESA's Columbus module on the International Space Station is being fitted with experimental hardware to track the passage of ships across the world's oceans. A pair of European-built signal receivers designed for wide-area vessel detection are being ferried to the orbital outpost aboard Japan's newly-launched H-II Transfer Vehicle.

The aim is to demonstrate space-based ship monitoring techniques which can then serve as the basis of operational services via satellite constellations.

Open ocean blind spots

All international ships over 300 tonnes, cargo vessels over 500 tonnes and passenger carriers of every size are mandated to carry Automatic Identification System (AIS) transponders which provide constantly-updated identification and navigation data.

The AIS system enables port authorities and coast guards to track seagoing traffic, but its VHF signals have a horizontal range of just 40 nautical miles (74 km). This means that AIS data is only available within coastal zones or on a ship-to-ship basis.

Traffic on the open ocean therefore represents a worrying blind spot to maritime and security organisations. But while AIS signals propagate only a short distance horizontally they do travel much further vertically – all the way up to space, where they can be picked up by satellite.

Overcoming signal collisions

Ships are mandated to carry AIS transponders

The problem is that AIS operates on a similar basis to mobile phone systems: ships within signal range form 'self-organising cells' within which they coordinate automatic sharing of frequencies. When looking down on the ocean from orbit however many of these cells become visible simultaneously, leading to numerous transmission collisions.

So the challenge of the COLAIS (Columbus AIS) project has been to develop sophisticated receivers which can de-scramble AIS messages as well as take account of Doppler shifting caused by rapid orbital motion relative to the sea surface.

One receiver has been developed by the Norwegian Defence Research Establishment (FFI) – also serving as the project's prime contractor – with Norwegian firm Kongsberg Seatex as subcontractor, and the second by Luxembourg-based company LuxSpace.

In-orbit demonstration

"Both groups are participating in various Agency AIS activities, with these receivers developed as an In-Orbit Demonstration project of ESA's General Support Technology Programme," says Frederic Teston, Head of ESA's Systems and Engineering Support Division. "This involves providing the European space sector with flight opportunities to prove new hardware. In this case the receivers were completed at a very rapid pace to reach orbit, the project having kicked-off only one year ago."

The International Space Station (ISS) represents an ideal platform for testing AIS receivers due to its orbit: its 400 km altitude is low enough to give a high probability of ship detection and it also passes across many of the world's most densely populated shipping lanes.

Norway's NORAIS and Luxembourg's LUXAIS receivers are due to reach Columbus when the H-II Transfer Vehicle (HTV) docks with the ISS next week. They will be connected to an AIS antenna constructed by the ARISS (Amateur Radio on the International Space Station) community and attached to Columbus with connecting hardware designed by Astrium. This equipment is scheduled to be flown to the Station by Shuttle on 12 November then installed on the Columbus exterior on a subsequent spacewalk.

The two receivers will be swapped every three months over a two year period. "They have several features," explains Karsten Strauch, ESA COLAIS project manager. "NORAIS and LUXAIS will demonstrate AIS message reception and decoding, as well as signal sampling as the basis of worldwide electromagnetic density maps, helping to plan future mission designs and strategies."